Treatment of paraffin hydrocarbons



" Patented July 5, 193a UNITED STATES AT NT OFFICE TREATMENT OF PARAFFINHYDRO CARBONS Hana 'lropsch, Chicago, 11]., assignor to' Universal OilProducts Company, Chicago, 111., a

poration of Delaware No Drawing. Application January 25, 1935, Serial-No. 3,474. Renewed January 14, I937 15 Claims.

This invention relates to the treatment of" parafiln hydrocarbons whichare normally gaseous including ethane, propane and the butanes. .In amore specific sense the invention is concerned with a process forconverting these low boiling members of the paraflin series ofhydrocarbons into their corresponding oleflns which contain two atoms ofhydrogen less per molecule and consequently have one double bond betweencarbon atoms.

There is a large commercial production of gaseous parafiln hydrocarbons.They occur in very large quantities in natural gas, particularly thosegases associated with the production oi.

15 crude oil and commonly known as casing head 'with diflerentcombinations of this general char- 15 gases and this supply is furtheraugmented-by the acter. The alternative combinations mentioned gasesproduced in'cracking oils for the production excludes salts of thehalogen acids which as a of gasoline although this latter type ofpyrolytrule have not been found to produce good proically produced gascontains substantial quantimoting effects.

vties'of olefins as well as parafflnic hydrocarbons. The mineralmagnesite from which magnesium 20 The greater part of the paraflin gasproduction oxide is conveniently prepared to furnish base is used merelyfor domestic and industrial fuel material for the present type ofcatalysts is most purposes and not as a source of hydrocarbon commonlyencountered ina massiveor earthy vaderivatives on account of theunreactive charriety and rarelyincrystal form, the crystals being acterof its components in comparison with their usually rhombohedral. Inmanymagnesites, Q5 olefinic counterparts. the magnesium oxide may bereplaced to the ex- In one specific embodiment the present inventent ofseveral percent by ferrous oxide. The tion comprises the dehydrogenationof gaseous mineral is of quite common occurrence and readily paraiiinhydrocarbons at elevated temperatures obtainable in quantity at areasonable figure.

in the presence of catalysts comprising essentially The pure compoundbegins to decompose to form 30 magnesium oxide supporting minor amountsof the oxide at a temperature of 350 0.. (663 F.) chromates and/ordichromates of lead, zinc, m'agthough the rate of decomposition onlyreachesa nesium, cadmium, iron, nickel, cobalt and alkali practicalvalue at considerably higher temperametals and'other chromates, forinstance thorium tures, usually of the order of 800 C. (1472F.)

chromate, along with still smaller proportions of to 900 C. (1652 F.)This n ineral is related to 35 selected sulfates, nitrates, acetates andother salts dolomite, the mixed carbonate of calcium and of these samemetals and preferably those of zinc, magnesium, this later mineral,however, not becopper and aluminum. ing of as good service as therelatively pure mag- In the present instance the catalyst mixturesnesite in the present instance. Magnesium car- 40 which are preferredfor selectively dehydrogenatbonate prepared by precipitation or otherchem- 40 ing the lower boiling paraflinic hydrocarbons ical methods maybe used alternatively, in place have been evolved as the result of alarge numof the natural mineral, this permitting its use as ber ofexperiments with catalysts having a dethe active constituent of massescontaining spachydrogenating action upon various types of hyingmaterials of relatively inert character and in drocarbons such as areencountered in the fracsome cases allowing the production of catalystsof 45 tions produced in the distillation of petroleum and othernaturally occurring hydrocarbon oil 3 mixtures. The criterion of anacceptable dehydrogenating catalyst is that it shall split oil.

'50 hydrogen without inducing either carbon separa- 55 motlng salts asgenerally designated in the prehigher efliciency and longer life.

To prepare the magnesium oxide for use as base material for preparingcatalysts for the process, the corresponding carbonate obtained eitherfrom natural sources or by precipitation reactions is preferably heatedfor variable periods of time at temperatures in the neighborhood of 800C. (1472 F.) which insures the decomposition of most of the carbonate tooxide. The

conditions of time and temperature employed in calcining any particularcarbonate mineral will depend, to a large extent, upon its physical and,to a smaller extent, upon its chemical composition. -Magnesite maycontain at times several per cent of ferrous oxide in isomorphousmixture with magnesium oxide and since it occurs in nature in a harderand more compact variety than the precipitated carbonate, it may requirefor both reasons different conditions of time and temperature to reducesubstantially all of it to the desired oxide. r

The mineral oxide of magnesium may sometimes be employed (this oxidebeing known as periclase) whenever the same is readily available and itsphysical properties as well as its content of impurities permits. Themineral oxide occurs in granular form or in definite cubic or 00-tahedral crystals and may contain in many cases besides relativelyinertsiliceous'gangue materials small amounts of iron and manganese replacinga portion of the magnesium. v

The deposition of the promoting oxide may be effected in a number ofways, any one of which is comprised within the scope of the invention.Thus, for example, lead chromate may be deposited upon magnesium oxideby stirring the magnesite in an aqueous solution of potassium chromateor dichromate and thereafter impregnating in-a solution of lead acetate.For the further addition of salts it may suflice to heat the filteredand washed particles containing chromate with other salt solutions suchas, for example. a fairly concentrated solution of zinc sulfate,duringwhich step some of the dissolved salt is occluded, after which themagnesite particles are again filtered and washed. The oxide containingthe desired amounts of promotingsubstance is then dried at a moderatetemperature to produce the final catalyst.

In lieu of the foregoing procedure the incorporation of the necessarypromoters may be ef- 'fected by successive additions of relativelyconcentrated solutions of the required promoting salts to solidmagnesium oxide until a paste of uniform consistency is obtained, afterwhich the water is evaporated to leave the salts deposited upon themagnesium oxide. process of addition comprises only well knownprocedures in the chemical art and may be varied to suit the needs ofany particular combination which has proven valuable in catalyticreforming operations.

In regard to the relative proportionsof magnesium oxide and promotingmaterials it may be stated in general that the latter are generally lessthan 10% by weight of the total composites.v

The effect upon the catalytic activity of the magnesium oxide caused byvarying the percentage of any given compound or mixture of compoundsdeposited thereon is not a matter for exact calculation but more one fordetermination by experiment. Frequently good increases in catalyticeffectiveness are obtainable by the deposition of as low as 1 or 2% of apromoting salt upon the surface and in the pores of the oxide, thoughthe general average is about 5%.

In practicing the dehydrogenation of paraflinic gases according to thepresent process a solid composite catalyst prepared according to theforegoing alternative methods is used as a filler in a reaction tube orchamber in the form of particles of graded size or small pellets and thegas to be dehydrogenated is passed through the catalyst am. being heatedto the proper temperature, usually within the range of from 400 Thus theto 750 C. (752-1382" F.) The most commonly used temperatures are around500 C. (900 F. to 1000" F.). The catalyst tube may be heated exteriorlyif desired to maintain the proper reaction temperature. The pressureemployed may be atmospheric or slightly superatmospheric of the order offrom 50 to pounds per square inch, though any large amount of pressurehas a tendency to depress the dehydrogenation reactionsdisproportionately to .the increase in capacity of the plant. The timeduring which the gases are exposed to dehydrogenating conditions in thepresence of the preferred catalyst is comparatively short, always below20 seconds .and frequently as low as from 4-8 seconds.

The exit gases from the tube or chamber may be passed through selectiveabsorbents to combine with or absorb the olefin or olefin mixtureproduced or the olefins may be selectively polymerized by suitablecatalysts, caused to allwlate other hydrocarbons such as aromatics ortreated directly with chemical reagents to produce desirable andcommercially valuable derivatives' After the olefins have been removedthe residual gases may be recycled for further dehydrogenating treatmentwith or without removal of hy-v drogen.

Members of the present group of catalysts are selective in removing twohydrogen atoms from a'paraffin molecule to produce the correspondingolefin without furthering to any great degree undesirable sidereactions, and because of this show an unusually long period of activityin service as will be shown in later examples. When,

however, theiractivity begins to diminish it is readily regenerated bythe simple expedient of oxidizing with air or other oxidizing gas atamoderately elevated temperature, usually within -the range employed inthe dehydrogenating reactions. traces of carbon deposits whichcontaminate the This oxidation effectively" removes surface of theparticles and decrease their efliciency. It is characteristic of thepresent types of catalysts that they may be repeatedly regen- Example IThe preparation of the catalyst was as follows:

. 50 parts by weight of magnesite burned one hour at 800 C. (1472 F.)and screened to 8-10 mesh was treated with 100 parts of a 1% solution ofchromic acid. The magnesium oxide. impregnated with the chromic acid wasthen dried and thereafter treated with 100 parts of a solutioncontaining 1% of cobaltous nitrate, 1% of lead results obtained by meansof gas analyses taken at indicated times from the start of the run.

" it was stirred for about hour at 50 C. The

. tower containing the pellets as filler at atmosY-Z to per hmir.

From the above data it will be seen that the dehydrogenationcorrespondsclosely to the calculated equilibrium mixture at 600 0.,(1112 F.) which should'contain approximately 33% hy-. drogen, 33% butaneand 33% butylenes. Substantially 50% of the original isobutane was'con-'verted intooleflns and hydrogen.

It is to be further observed that the catalytic activity was maintainedsubstantially constant for the period of a run of approximately 10 days.Example II The catalyst used" in this case consisted of granulatedmagnesium oxide supporting lead chromate and ferric sulfate. To make thecatalyst, parts by weight of a previously prepared material containinglead chromate was added to 150 parts of a 1% ferric sulfate solution, inwhich catalyst particles were then filtered from the solution and driedat 300 C. (572 F.)

Using small pellets of the above oxide mixture n'-butane was passedthrough a treating pheric pressure and temperatures of about 600 C..(1112' F.) with a space velocity oi from 45 The following table showsthe nature of the results obtained by means of gas analyses taken atindicated times from the start of the run.

Composition of 'dehudrogenated gases Time after start, hours 40 M 1% nButane, percentl8. 6 l8. 3 17. 5 l6. 0 Propylene, percent 12. 3 ll. 4 9.8 9. 3 Eth ene, perccn 2. 3 2. 4 p 4. 7 2. 2 Parafilns (mainly n utane),D ree 41. 0 42. 9 43. 7 50. 1 Hydrogen, percent 25.8 25.0 24.3 22.4

It is again observable mat the catalytic activity was maintainedsubstantially constant for a period of a run which was in this case 5days.

Example III A catalyst was prepared whichcontained magnesium chromateand zinc sulfate supported on magnesium oxide by the following method.45

parts by weight of magnesium nitrate, anequal weight of magnesiumchromate arid-10 parts by weight of zinc sulfate were separatelydissolved in small amounts of water, the solutions mixed and thecomposite evaporated to dryness. The drypowder was heated at- 250 'C.(482 F.) for one hour. The material was then-ground and sized toconserve particles of from 6-10 mesh diameter.

Using small pellets of the above oxide mixture madeby moistening andcompressing and later drying as in the previous examples, propane waspassed through a treating tower containing the The following table showsthe nature of the results obtained by means of gas analyses taken I atthe same indicated times from the start of the run. I

' oxide and a minor proportio o 3,139,787 Cmnpositionof dehydrooenatedoases Composition of dehydrogenated gases Time alterstart hours 40 so15o 25o ut e e. pewe t m m m tigg gg zfiggg it 8 83 4 8 3 gglfiexibutylenes and propylene, percent. Ethylene percent u 3 2 3 3 5 6 3 1 Y PParaflin'skmainly 'fimplifli'ifi c'eh 64's 04's 03's 01'1 Parafllns(mainly i-butane), percent 35.0 37. 1 35.4 38.4 L Hydrogen, percent 31.031.9 30.0 29.0 Hymgm'peimnt There was substantially no change in thecatalytic activity oi! the catalyst used over a period of 6 days ofcontinuous operation.

The f oregoing specification and'examples are suflieient to show thatthe invention has intrinsic value when practiced in the art, but neithersection is to be construed as imposinglimitations upon the scope of theinvention, as both are given for illustrative purposes only.

I claim as my invention:

1. A process for converting normally gaseous parafllns into oleflnswhich comprises dehydrogenating'the same in the presence of magnesiumoxide admixed with minor proportions of a chromate and a metal salt ofan oxygen-containing acid selected from the group consisting ofsulphuric, nitric and acetic acids.

- 2. A process for converting normally gaseo paraflins into olefinswhich comprises dehydrogenating the same in the presence of magnesiumoxide admixed with minor proportions of a chromateand a metal sulphate.

3. A process for converting normally gaseous parafilns into oleflnswhich comprises dehydrogenating the same in the presence of magnesiumoxide admixed with minor proportions of a chro- -mate and ametal'nitrate.

4. A process for converting normally gaseous 'paraflins into olefinswhich comprises dehydrogenating the same in the presence of magnesium :7oxide admixed with minor proportions of lead chromate and zinc sulphate.

6. A catalyst suitable for use in the dehydrogenation of hydrocarbonscomprising a major proportion of magnesium oxide admixed withminorproportions of a chromate and a metal salt oi an oxygen-containingacid selected from the group consistingoi sulphuric, nitric and aceticacids.

. .7. A catalyst suitable .Igr use in the dehydrogenation ofhydrocarbons comprising a major proportion of magnesium oxide admixedwith minor proportions oi achromate. and a metal sulphate. I

8. A catalyst suitable tor use in the dehydrogenation of hydrocarbonscomprising a major proportion of-magnesium oxide admixed. with minorproportions of a chromate and a metal nitrate. A 9. A catalyst suitablefor use in the dehydrogenation 0'! hydrocarbons comprising a majorproportion of magnesium oxide admixed with minor, proportions of achromate and a metal acetate.

10. A process for converting normally gaseo paraflins into olefins whichcomprises dehydrogenating the same in the presence of a'catalyticmixture of a major proportion of magnesium chromates' 11. A process forconverting normally gaseous paraflins into oleflns which comprisesdehydrof-genating the same in the presence of magnesium oxide admixedwlth less than 10% by weight of lead chromate. v

12 A process for dehydrogenating hydrocarbons whichdcomprises subjectingthe hydrocarbons under dehydrogenating'conditions to theiaction of amagnesium oxide catalyst containing lead chromate in relatively smallbut sufllcient amount to promote the catalytic activity of the magnesiumoxide.

13. A process tot-1 dehydrogenating hydrocarbons which comprisessubjecting the hydrocarbons to delaydi ogenating conditions in thepresence of a magnesium oxide catalyst containing a hromate inrelatively small but sufllcient amount to promote the catalytic ativttyof the oxide. i 1

14. A piocess tor dehydrogenating hydgocarhens which comprisessubjecting the hydgocav bcns to dehydrogenating conditions in thepreseiice of a magnesium oxide catalyst, said catalyst furthercontainlnga relatively small amount of a metallic oxygen-containing salt selectedfrom the group consisting of the sulfates, nitrates and acetates ofzinc, copper and aluminum.

, 15. The process as defined in claim 13 further HANS TROPSCH. l5 7

